Make Reposition Work for Non-new Cards

> The position info is now shown for even already introduced cards. Would it be possible to also make “Reposition” feature work for non-new cards? It’s useful for those of us who share our decks from the same account we normally use for syncing.
> The use case is same one that others described in previous “show position for Non-new cards” threads, i.e. having a certain order for cards is useful in some situations.
> As you study your cards, if you notice some questions are missing there’s no way for you to know whether the deck author made those cards or not unless you go to the Browse screen to search. And as deck authors, we may want to add things later, switch the order of cards after already personally studying through them.

Originally reported on https://forums.ankiweb.net/t/make-reposition-work-for-non-new-cards/51207

No files, tests, or entry points are identified in the issue. First locate the existing Reposition implementation and the code that distinguishes new from non-new cards, then determine the expected ordering behavior for already studied cards and add coverage for the reported use case.

Written by the indexing model from the issue text.